Liquid dielectric coolant plays a dual role as an insulating medium between the energized parts and as well as a coolant in the performance of electrical equipments particularly in power distribution transformers, high frequency and high voltage transformers and in electrical apparatus or appliances. The mineral oil and silicone fluid are the most common liquid dielectric coolants used in power frequency transformers and high frequency transformers. The performance of the liquid dielectric coolant or liquid insulation has been evaluated for its electrical, physical, chemical and thermal properties by considering various factors such as high breakdown strength, good oxidation stability or good ageing resistance, high flash point, low viscosity, good thermal conductivity for good heat dissipation, good compatibility with solid insulating materials/other materials used in electrical transformers, low dissipation factor, etc. The liquid dielectric strength defines the ability to resist electric breaks at certain frequencies of electrical power. The liquid dielectric strength is measured as the minimum electric voltage, which is required for formation of an arc between two electrodes. Recent developments in the formation of liquid insulation have led to the development of a process to extract liquid dielectric coolant from the rice bran oil, which is suitable for both power frequency and high frequency electrical applications.
Various types of conventional liquid dielectric coolants are known in the prior art, wherein most of them use mineral oil and silicone fluid as liquid insulation in power frequency transformers and in the high frequency transformers. Typically, the conventional methods use mineral oil composition for power frequency applications. The liquid dielectric coolant of the mineral oil has relatively high value of breakdown voltage for power frequency applications. However, the use of mineral oil composition as a liquid insulation does not provide support for high frequency applications, as the breakdown voltage strength drops by one third at hundred kHz (Kilo Hertz) and also the liquid insulation of the mineral oil has low flash point and is non-biodegradable.
Conventional methods use the silicone fluid as a liquid insulation for high frequency applications. The liquid dielectric coolant of the silicone fluid operates at higher temperature for high frequency applications. However, the use of silicone fluid as a liquid insulation does not provide support for power frequency applications due to fast degradation by corona effect.
Hence, there is a need for a process to extract liquid dielectric coolant, which is suitable for both power frequency and high frequency electrical applications.